1. Field of the Invention
The present invention relates to an exposure condition decision support system and method that support decision on an exposure condition of a radiation imaging system.
2. Description Related to the Prior Art
In a medical field, a radiation imaging system, for example, an X-ray imaging system using X-rays is widely known. The X-ray imaging system is constituted of an X-ray generation device for emitting the X-rays to a patient's body, and an X-ray image capturing device for taking an X-ray image of the body. The X-ray image capturing device has an X-ray image detector, which detects the X-ray image as an electrical image. As the X-ray image detector, the one using an FPD (flat panel detector) is in practical use. The FPD has a detection surface in which pixels are arranged in a matrix. Each pixel accumulates signal charge by an amount corresponding to the amount of the X-rays incident thereon. The FPD detects the X-ray image on its detection surface by accumulation of the signal charge on a pixel-by-pixel basis, and outputs the X-ray image as digital image data.
The X-ray imaging system requires determination of an exposure condition before performing radiography. The exposure condition refers to various settings necessary for operation of the X-ray generation device and the X-ray image capturing device. The exposure condition includes, for example, “exposure menu” relating to exposure contents such as an exposed body portion and an exposure direction, “body information” relating to physical information on the patient's body such as body thickness, and “exposure parameters” being a setup condition required for generation of the X-rays from the X-ray generation device, such as tube voltage and tube current-time product.
As to the exposure parameters e.g. the tube voltage and the tube current-time product, their proper values vary depending on a combination with the exposure menu and the body information. Thus, not only knowledge about the exposure condition but also sophisticated skill reinforced by experience is required of a radiological technician who determines the exposure condition. However, a skill level varies from technician to technician, and inevitably, there are relatively low-skilled radiological technicians. As is often the case, the low-skilled radiological technician takes long time to determine the exposure condition. The low-skilled radiological technician sometimes makes a mistake in the exposure condition and obtains a poor-quality image unsuitable for diagnosis. This requires another exposure to be made.
Conventionally, to allow determination of the proper exposure condition regardless of the skill level of the radiological technician, it is proposed to determine the exposure condition used in present radiography by reference to the exposure conditions used in past radiography. For example, Japanese Patent Laid-Open Publication No. 2004-105437 discloses an X-ray imaging system that stores X-ray images (hereinafter called past images) obtained in the past radiography and quality evaluation data of each past image in relation to each other, and uses the quality evaluation data as a reference to determine the exposure condition. Japanese Patent Laid-Open Publication No. 2009-060939 discloses an X-ray imaging system that receives input of the body information as a retrieval query, and the past exposure conditions are displayed in decreasing order of compatibility with the body information or decreasing order of use frequency. US Patent Application Publication No. 2004/0227821 corresponding to Japanese Patent Laid-Open Publication No. 2004-337232 discloses an X-ray imaging system that stores a failure image as an invalid image unusable for diagnosis.
According to the Japanese Patent Laid-Open Publication Nos. 2004-105437 and 2009-060939, the exposure condition of the present radiography can be determined by reference to the exposure conditions of the past images. The past images, however, include failure images and re-exposure images, in addition to model images suitable for diagnosis. The failure image denotes a poor-quality image unusable or barely used for diagnosis. The re-exposure image denotes an image obtained after the failure image by another exposure. Generally speaking, most of the failure images and re-exposure images are taken by the low-skilled radiological technician. Thus, the failure images and the re-exposure images should not be used as the reference to obtain a high-quality image.
By the way, according to the Japanese Patent Laid-Open Publication No. 2004-105437, the quality evaluation data is listed on a monitor together with the past images and the exposure conditions. Thus, checking the quality evaluation data allows avoiding the use of the failure image. In the Japanese Patent Laid-Open Publication No. 2009-060939, the past images and their exposure conditions are displayed on the monitor in decreasing order of the use frequency. The lower the use frequency, the more likely the past image is to be the failure image. Thus, choosing the past image of the high use frequency allows avoiding the use of the failure image. If the X-ray imaging system disclosed in the Japanese Patent Laid-Open Publication No. 2004-105437 or 2009-060939 is combined with the technique of the US Patent Application Publication No. 2004/0227821, by which the failure image is not displayed as the invalid image, it is possible to exclude the failure images from the reference to determine the exposure condition. However, none of the Japanese Patent Laid-Open Publication Nos. 2004-105437 and 2009-060939 describes exclusion of the re-exposure images from the reference.